Plant growth substances (e.g., plant hormones, phytohormones, or growth regulators) influence a range of plant developmental processes including stem elongation, germination, dormancy, flowering, sex expression, enzyme induction, fruit, set and qualify, as well as leaf and fruit senescence.
S-(+)-Abscisic acid is a naturally-occurring hormone found in all higher plants (Cutter and Krochko, Formation and Breakdown of ABA, Trends in Plant Science, 4:472-478 (1999); Finkelstein and Rock, Abscisic acid Biosynthesis and Signaling, The Arabidopsis Book, ASPB, Monona, Md., 1-52 (2002)). S-(+)-Abscisic acid is reported to be found in all photosynthetic organisms (Cutler and Krochko, 1999; Finkelstein and Rock, 2002). S-(+)-Abscisic acid is involved in many major events of plant growth and development including dormancy, germination, bud break, flowering, fruit set, general growth and development, stress tolerance, ripening and abscission.
Commercial formulations comprising abscisic acid are used in agriculture for various purposes, such as improving stress tolerance, slowing growth rate, adjusting flowering phase and other purposes. Abscisic acid has also been reported to possess insect inhibition qualities (see U.S. Pat. Nos. 4,434,180 and 4,209,530).
S-(+)-Abscisic acid may be combined with a cytokinin such as benzyladenine. Treating a seed with benzyladenine has been shown to improve the emergence rate of seeds treated with S-(+)-Abscisic acid (see U.S. Patent Publication No. 2009/0137391).
Crop management comprises many aspects such as treating seed prior to planting, treating crops during various phases of plant growth (foliar or drench application) and post-harvest application to extending shelf-life.
Seed treatment has been found to be beneficial for hundreds of years. Seed treatment is gaining importance in the farming community as the cost of seed (including genetically modified seed) is on the rise increasing the need to protect seeds during storage as well as to protect them from adverse environmental conditions after planting and during germination or emergence of seedlings. Seed treatment includes coating seed with various pesticides including but not limited to fungicides, herbicides, insecticides, plant growth regulators and other nutrients. One of the major roles of seed treatment is to minimize the economic impact that might occur due to potential infestation and adverse growth conditions that could result in reduced yields as well as lower product/grain quality. Crop seed treated with various pesticides and plant growth enhancers include cereals (e.g., corn, sorghum, and wheat), legumes (e.g., soybean, peanut, and various beans) and vegetables (e.g., carrot, spinach, and tomato).
Topical (foliar) applications and or drench applications are carried out to protect growing crops from diseases and pests as well as to improve crop growth, yield and quality.
Plant growth regulators may be formulated in at least six different types of formulations: (1) solutions; (2) wettable powders; (3) soluble powders; (4) tablets; (5) water-dispersible granules; and (6) water soluble granules. In order to use such formulations, they must be diluted in an aqueous medium prior to conventional spray application. Each of the conventional types of formulations has disadvantages, therefore, research to develop improved delivery systems for plant growth regulators continues. Some of the disadvantages of conventional formulations with specific reference to abscisic acid are discussed below.
One of the problems associated with current abscisic acid formulations for use in agriculture is the relatively poor solubility of abscisic acid in water: only about 3grams per liter, or alternatively, 0.3% by weight can be dissolved in water. A concentration of about 3000 ppm is the highest concentration that can be achieved in pure water at room temperature. Abscisic acid solubility in hard water (water with a high mineral content) is even less. These low strength solution formulations (which contain a low concentration of abscisic acid) require larger packaging, more storage space, and higher associated transportation, warehousing, and container disposal costs. Further, these formulations are not suitable for use in seed treatment because excessive carrier from the formulation may make the treated seed sticky and not suitable for conventional planters. In addition, higher seed moisture can also encourage mold growth and impair germination. These problems might increase as the formulation is tank-mixed with other seed treatment formulations containing insecticide(s) and fungicide(s). While abscisic acid exhibits somewhat better solubility so some organic solvents, liquid formulations of abscisic acid in organic solvents are often undesirable due to flammability, toxicity, or pollution considerations. In addition, abscisic acid is known to exhibit poor storage stability in solvent based formulations, cause hydroxylation inactivation of 8′ and 9′ methyl groups in plants (see U.S. Pat. No. 6,004,905) and cause sunlight induced degradation and isomerization of active 2-cis, 4-trans-S-(+)-Abscisic acid to the inactive 2-trans, 4-trans-S-(+)-Abscisic acid isomer (Kamuro, The Present Situation and Problems in the R&D for Practical Uses of Abscisic Acid, Plant and Chemical Regulation, 29:155-165 (1994)). Organic solvents may also exhibit an adverse effect on seed germination.
A soluble powder formulation is one which, when mixed with water, dissolves readily in water and forms a true solution. Once the solution is formed, no further mixing or agitation of the solution is required.
A wettable powder formulation is a dry, finely ground formulation. In this formulation, the active ingredient is combined with a finely ground dry carrier, usually a mineral clay, along with other ingredients that enhance the ability of the powder to be suspended in water. Upon mixing the wettable powder with wafer, a suspension is formed which is then applied to crops by spray equipment.
The primary disadvantage of wettable powder and soluble powder formulations is that they tend to produce dust upon handling, such as when pouring, transferring or measuring them. This dust may pose health hazards. Further, powder formulations tend to wet poorly and also solubilize slowly upon addition to water. Powder formulations thus take longer to wet, disperse, and solubilize in the tank-mix. Formation of lumps or partially solubilized spray solutions will lead to uneven distribution of the plant growth regulator with the potential for reduced field performance. Wettable powder formulations will also leave undesirable insoluble residues both in storage tanks and on sprayed foliage and fruit.
Tablet formulations are pre-measured dosage delivery systems. They are useful in small areas, or for ornamental purposes. Tablet formulations may be effervescent and dissolve in water over a period of two to ten minutes depending upon the type and size of the tablet. However, tablets deliver only between 0.1-1 g of active ingredient per tablet and, therefore, are not an ideal product form.
Water dispersible granules are also known as wettable granules or dry flowables. This type of formulation is similar to a wettable powder, except that the active ingredient is formulated in the form of water dispersible granule. Water dispersible granules upon addition to water and mixing form suspensions. The resulting suspension must be agitated for a period of time in order to fully disperse the active ingredient. Agitation or by-pass recirculation of the formulation must also be maintained during application to ensure uniform suspension and spray coverage. The quality of water dispersible granules is highly dependent on the manufacturing process and the active-ingredient; and can result in low yield recoveries, poor attrition resistance leading to dust potential, high manufacturing cost and poor dispersion. Generally, sprays of dispersed water-dispersible granular formulations leave undesirable insoluble residues on the treated foliage and fruit. Water-dispersible granules may not be directly added to seed treatment mixtures and generally pre-mixing in a small portion of wafer may be necessary. Water-dispersible granules can become hardened over time, thus resulting in poor dispersibility and solubility of the active ingredient. Dust and caking may be problems with certain water-dispersible granules and powder formulations. Water-dispersible granules may thus not be ideal product forms for seed treatment.
A soluble granule formulation is one which, when mixed in water, dissolves readily in water and forms a true solution. Once the solution is formed, no further mixing or agitation of the tank-mix is required. U.S. Pat. No. 6,984,609 B2 discloses water-soluble granular compositions of at least one plant growth regulator, preferably a gibberellin, a disaccharide and a surfactant. U.S. Patent Application Publication No. 2008/0254988 discloses a composition for a 5% solution formulation as well as a 20% water soluble granular formulation for S-(+)-Abscisic acid. The granules must be solubilized in water prior to addition to seed and foliar treatment mixtures. However, the solubility limit of S-(+)-Abscisic acid in the tank-mix is only up to 3000 ppm. Thus, this type of formulation is not ideal for S-(+)-Abscisic acid and its use in seed-treatment mixtures.
Therefore, there is still a need for an S-(+)-Abscisic acid formulation that overcomes the disadvantages of the prior art formulations.